Thin-film magnetic recording disks and disk drives are commonly used for storing a large amount of data in magnetizable form. Over the last decade, magnetic recording has become the predominant technology for the storage of digital information in modern computer systems.
Magnetic recording generally is accomplished by the relative motion between a magnetic medium and a magnetic recording head. A magnetic recording head consists of a small electromagnet with a gap facing the magnetic medium. During writing, a current is applied to the windings of the electromagnet, thus creating a fringing field at the head gap and magnetizing the magnetic medium according to the direction of the current applied to the head. During reading, the flux from the magnetic medium is intercepted from the head core, inducing a voltage pulse in the coil of the read head.
FIGS. 1A and 1B illustrate a typical disk drive. FIG. 1A is a top plan view of the disk drive, and FIG. 1B is a side view of the disk drive. The disk drive 10 generally includes a magnetic disk 11 and a disk head 16 for writing and reading information to and from the magnetic disk 11. The disk head 16 may include a read/write element 12 and a slider 13. The disk head 16 is connected to a suspension arm 14, which is, in turn, connected to a rotary actuator 15.
Two widely used methods to store and retrieve data are commonly referred to as contact start/stop (CSS) and ramp load/unload. In each design, rotation of the magnetic disk produces an air layer between the head and the surface of the disk. In this state, recording or reproduction of data is performed. Occasionally, however, a slight change in altitude of the head renders the load on the head non-uniform, causing contact to occur. Such contact may result in damage to the head and the surface of the magnetic disk for both CSS and ramp/load unload designs.
At the end of the operation, the rotation of the magnetic disk is stopped. In contact start/stop (CSS) designs, the head is allowed to rest on a laser textured landing zone on the surface at the edge of the magnetic disk. In ramp load/unload designs, the sliding head is completely removed from the disk prior to the air bearing collapsing. However, occasional impact between the sliding head and the magnetic disk still occurs, particularly during start-up (loading) conditions before the air film has stabilized.
To prevent the wear of the magnetic disk caused by the contact with and sliding on the head, a lubricant layer is provided on the surface of the magnetic disk. A common lubricant used in magnetic disks is perfluoropolyether (“PFPE”). To increase the wear resistance of the magnetic disk and to protect the magnetic material from the corrosive effect of the PFPE lubricant, a protective layer is sometimes provided between the magnetic medium and the lubricant layer. The protective layer may include amorphous carbon, diamond-like carbon, and other materials.
Due to the prevalent use of computers, increases in the areal data storage density of a magnetic disk have continued rapidly and unabatedly for almost 40 years. The trend towards high recording densities is expected to continue. For example, the current areal density is about 10 gigabytes per square inch. The next generation disks are going to have an areal density of about 50 gigabytes per square inch. In a few years, the areal density is expected to exceed 40 gigabytes per square inch. To achieve a high recording density, the magnetic head should be positioned as close as possible to the surface of the magnetic medium. The distance between the tip of the magnetic head and the surface of the magnetic medium is referred to as “flight height.” For example, to achieve an areal density of about 10 gigabytes per square inch, a flight height in the range of about 10-15 nm is required. If an areal density of 40 gigabytes per square inch is desired, the flight height should be further decreased to about 3.5 nm. This means that the thickness of the lubricant layer (or film) and the thickness of the protective layer should sum to about 3 nm or less. Consequently, the reliability of the head-disk interface becomes more dependent on the life and performance of the lubricant film as the conquest for higher density disks continues. In other words, the characteristics of the lubricant film, such as its physical, chemical, and tribological properties, have a critical impact on the performance of such high density disks.
First, the lubricant film or layer should last for the lifetime of the drive. If the lubricant layer wears away prematurely, the disk drive would fail accordingly. Furthermore, the lubricant layer should be resistant to chemical degradation. Chemical degradation of the lubricant layer can be induced by thermal decomposition, catalytic reaction with solid surfaces, and mechanical shearing due to high-speed contact with the disk head.
In addition to chemical stability, a major challenge in developing disk lubricant systems is to provide adequate durability without increasing stiction to unacceptable levels. During the lifetime of a magnetic disk, the disk head goes through thousands of stop-and-start cycles. If the static friction forces between the disk head and the magnetic medium become too large, the drive motor may not develop sufficient torque to restart disk spinning. This may lead to failure of the disk drive.
As mentioned above, PFPEs have been used extensively to form a lubricant film in a magnetic recording medium. PFPEs are relatively expensive. Therefore, cheaper alternatives are more desirable. Although PFPEs have good thermal stability, they decompose readily when they are in contact with Lewis acids. This is an important consideration because the head often is fabricated from an Al2O3/TiC composite, and Al2O3 can be converted to AlF3, a strong Lewis acid. This formation of AlF3 leads to chemical degradation of PFPE lubricants. Moreover, use of chlorofluorohydrocarbons (“CFCs”) as solvents generally is involved when PFPEs are applied to a magnetic medium as PFPEs are not compatible with many other hydrocarbon based solvents. CFCs have detrimental effects on the ozone layer, and use thereof should be avoided, if possible.
In view of the foregoing discussion, in order to meet the challenge of the information age, there is a need to develop magnetic recording media with a lubricant layer that is more chemically and mechanically robust to withstand high shear rates and harsh environments. The lubricant layer should allow decreased flight height so that higher areal densities may be achieved. Furthermore, it is desirable that such lubricant be relatively inexpensive, environmentally friendly, that no CFCs be used in forming the lubricant layer, and that the materials used in the lubricant layer be compatible with a range of hydrocarbon solvents.